The invention relates generally to the field of data communications and, more particularly, to a system and method for improving the performance of a data loop.
A data network provides a medium that enables devices to send data to and receive data from other devices. Devices that are typically connected to a data network include computers and data storage systems.
For example, in a data storage system large amounts of information may be stored magnetically or optically on one or more disk drive-based devices (hereafter referred to for convenience as “disks”). These disks may be in locations that are remote from other disks in the system and from devices that need to access the information. Using a data network, a device such as a central computer or a server may access the information stored on each of the disks.
Several topologies are common for attaching a server to its disks. For example, a server may attach directly to the disks through several point-to-point links. One advantage of this topology is that a disk does not share its link with other disks. As a result, information may be sent to and received from a disk with low latency. However, this approach may be relatively expensive in a system that includes a large number of disks, as the server must provide an interface for each of the links.
Alternatively, a server requiring access to a large number of disks may attach to a switch fabric. This topology enables the server to access multiple drives from a single attachment point. In a switch topology, the switch examines each data frame from the server and, based on information associated with the frame, forwards the frame to one of the disks attached to the switch. Thus, because the switch forwards data directly to the appropriate destination, a switch may still provide relatively low latency data transfers to and from each disk. A disadvantage of this topology, however, is the relatively high cost of a switch.
Another common topology for connecting servers and drives is a loop topology. This topology enables a server to connect to multiple drives through a single point of attachment without incurring the expense of a switch fabric. In the loop topology, the data frame passes through each disk in turn until the destination disk is reached. Thus, a disadvantage of a loop topology compared with the other topologies is its longer latency.
As the above discussion illustrates, each of these topologies have one or more disadvantages. Accordingly, a need exists for improved methods of transferring data between devices.